A bit on the more unusual side, one thing my son and I found very instructive on "lower level" concepts is the fact that within PICO-8, which is already a very user friendly high-level environment, you can use peek(), poke(), memset(), memcpy and similar functions on any memory address that PICO-8 uses. Literally all the capabilities that PICO-8 gives you, it exposes memory for it and explains the conventions it uses to read/write that memory, so that you could do it yourself. We were able to make a simplistic "paint" program that draws a pre-drawn cursor sprite and changes pixels whenever you drag the mouse, all using memset(), peek() and poke(), and avoiding line(), spr() and doesn't use any Lua tables. It entirely does this by reading and writing memory. It was a fun experience in learning certain useful low-level memory concepts.